Ulcerative colitis is a chronic inflammatory disease of unknown etiology afflicting the large intestine. The course of the disease may be continuous or relapsing, mild or severe. The earliest lesion is an inflammatory infiltration with abscess formation at the base of the crypts of Lieberkuhn. Coalescence of these distended and ruptured crypts tends to separate the overlying mucosa from its blood supply, leading to ulceration. Signs and symptoms of the disease include cramping, lower abdominal pain, rectal bleeding, and frequent, loose discharges consisting mainly of blood, pus, and mucus with scanty fecal particles. A total colectomy may be required for acute, severe or chronic, unremitting ulcerative colitis.
Neither the initiating event nor the sequence of propagating events that lead to and sustain colitis have been fully elucidated (1). Nevertheless, it is increasingly clear that a dysfunctional immune-response, involving Toll-like receptor 4 (TLR4) and components of normal gastrointestinal gram-negative bacteria appear to play a key role in the pathogenesis of colitis (2). Thus, an early step is macrophage antigen presentation (1), a process involving the CD14/TLR4 complex, which leads to interferon (IFN) production and release, as well as T lymphocyte secretion of IL-2. IFNs activate macrophages to produce a variety of cytokines, including TNFα and IL-1, that upregulate endothelial cell adhesion molecules (ECAMs). Chemokines such as IP-10 are also important in colitis (3) and have been implicated in studies of the myeloid cell-specific Stat3-deficient mouse, which is one of several experimentally induced, Th1-mediated models of Crohn's disease (CD) and UC. The Stat3-deficient mouse model also implicated TLR4 in disease expression, defective IL-10 signaling, and aberrant production of IL-12p40. Pro-inflammatory cytokines activate leukocytes and induce increased expression of ECAMs (5, 6) leading to leukocyte recruitment and extravasation via a well described adhesion cascade (7). Thus, in sum, the aberrant immune/inflammatory response is characterized by increased expression of TLR4, pro-inflammatory cytokines, chemokines, and ECAMs as well as enhanced interactions between leukocytes and hyperadhesive colonic microvasculature.
Tumor necrosis factor alpha, or TNFα, is a cytokine that is released primarily by mononuclear phagocytes in response to a number of immunostimulators. When administered to animals or humans, it causes inflammation, fever, cardiovascular effects, hemorrhage, coagulation, and acute phase responses similar to those seen during acute infections and shock states. Excessive or unregulated TNFα production thus has been implicated in a number of disease conditions, including: endotoxemia and/or toxic shock syndrome, cachexia, and adult respiratory distress syndrome (ARDS). TNFα appears to be involved in bone resorption diseases, including arthritis. TNFα also plays a role in the area of chronic inflammatory diseases, inducing angiogenesis in inflammation and reperfusion injury following ischemia. TNFα has pro-inflammatory activities, which mediate tissue injury in several important disorders including but not limited to, myocardial infarction, stroke and circulatory shock. Of specific importance may be TNFα-induced expression of adhesion molecules, such as intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and endothelial leukocyte adhesion molecule-1 (ELAM-1; a/k/a E-selectin), on endothelial cells. TNFα blockage has been shown to be beneficial in rheumatoid arthritis and Crohn's disease.
The above observations have led to the development of several therapeutic approaches that seek to diminish colitis (and related diseases) by attenuating the immune/inflammatory response. These approaches include the use of MAbs to TNFα (8), MAbs to ECAMs (e.g. MAbs to VCAM-1 (9), MAbs to leukocyte P2 integrins (10), and compounds that block the expression of ECAMs at the transcription level (11)).
Methimazole (MMI) is widely used clinically for the treatment of autoimmune Graves' disease or primary hyperthyroidism (12) and has been shown to be effective in treating several other forms of autoimmune disease, including psoriasis in humans (13), systemic lupus (14), autoimmune blepharitis, autoimmune uveitis, thyroiditis, and diabetes in murine experimental models (15-18). Several observations suggest that MMI may also affect ECAM expression and thus could be a potential anti-inflammatory compound. Specifically, it has been reported that (a) Graves' disease patients treated with MMI have reduced levels of circulating soluble E-selectin and soluble VCAM-1 (19) and (b) MMI decreases colonic mucosal damage in a rat model of experimental colitis (20). An effort to identify derivative compounds with greater anti-immune efficacy than MMI, led to the finding that phenyl methimazole (compound 10, C-10), a tautomeric cyclic thione, was 50 to 100-fold more potent and a far more effective agent in experimental models of lupus and diabetes (18, 21).
The observations regarding MMI and C-10 led us to probe the hypothesis that C-10 can reduce pathological inflammation. In a recent study, we used an in vitro model of inflammation and found evidence in support of this hypothesis. Specifically, we found that C-10 can reduce TNFα induced leukocytic cell adhesion to endothelial cells via inhibition of TNFα induced VCAM-1 and E-selectin expression (22). This finding, combined with the fact that TNFα and VCAM-1 have been implicated in the pathogenesis of colitis (1, 8), and the fact that therapies that inhibit the inflammatory cascade have proved quite successful in the treatment of colitis (8, 9), led us to probe the use of C-10 as a therapeutic for colitis. For this study, we used the DSS induced murine model of colitis, which is a well established model of human colitis (23). This model is characterized by dysregulated inflammatory response indicated by presence of edema, infiltration of inflammatory cells, and extensive mucosal damage. We used this model to assess the effect of C-10 on the gross pathology of colitis as well as on the expression of key receptors, cytokines, chemokines and ECAMs that have been implicated in the pathogenesis of colitis.